Any errors from calling `bpy.ops.render.render(write_still=True)` would
be suppressed, making it impossible to know what went wrong.
Now the operator now reports errors when run via `exec` which mainly
occurs when the operator is called from scripts.
Interactively rendering via `invoke` is left as-is since users can see
the error in the UI and showing a popup error is disruptive.
7e99470a85